A vehicle with an engine may include an evaporative emission control system coupled to a fuel system in order to reduce fuel vapor emissions. For example, an evaporative emission control system may include a fuel vapor canister coupled to a fuel tank which includes a fuel vapor adsorbent for capturing fuel vapors from the fuel tank while providing ventilation of the fuel tank to the atmosphere.
Leak testing may be periodically performed on such evaporative emission control systems in order to identify leaks in the system so that maintenance may be performed and mitigating actions may be taken in order to reduce emissions. In some examples, natural vacuum approaches may be used to perform leak detection in evaporative emissions systems in vehicles, e.g., in hybrid electric vehicles.
However, the inventors herein have recognized that due to limited engine run time in hybrid electric vehicles, sufficient natural vacuum may not be available for leak testing while the engine is running. Further, engine-off natural vacuum (EONV) leak detection approaches use a passive system which is dependent on driver behavior and powertrain type. Further, in such an approach, too little or too much heat rejection may skew the results of leak test. Further, in plug-in hybrid vehicle applications, the engine may or may not combust to generate sufficient heat so that EONV approaches may not be viable.
Active leak testing systems, which use powered pumps to provide vacuum to the fuel system for leak testing, may consume a significant amount of power in order to provide sufficient vacuum to perform leak tests. For example, this power consumption may reduce the time the test can execute during engine off conditions, e.g., after a key off event. Further, this energy draw may reduce how long the evaporative test can execute during engine off conditions in applications where battery power is limited, e.g., in hybrid electric applications.
Further, the inventors herein have recognized that it may be advantageous to perform leak test using pressure increases instead of or in addition to leak testing which uses vacuum increases in the fuel system. For example, seals in the fuel system may behave differently under pressure versus vacuum and thus it may be desirable to employ both a vacuum based and a pressure based phase to identify leaks in a fuel system with greater accuracy.
In one example approach, in order to at least partially address these issues, a method for a vehicle with an engine comprises, during an engine off condition delivering fuel from a fuel tank into a reservoir while the fuel tank is vented to atmosphere, and sealing the fuel tank from atmosphere and indicating a leak based on pressure in the fuel tank. The method may further comprise, during an engine off condition, delivering fuel from the fuel tank into the reservoir for a duration while the fuel tank is sealed from atmosphere, and indicating a leak based on vacuum in the fuel tank.
In this way, an active leak testing approach may be used in a hybrid vehicle application with limited engine run time while reducing an amount of time a pump is used thus reducing power consumption costs associated with the pump. For example, by using a fuel reservoir to assist in pressure and vacuum generation for leak testing in a hybrid vehicle, an amount of time the pump is operated to generate sufficient vacuum or pressure in the fuel system for leak testing may be reduced.
Further, in such an approach, pressure increases in the fuel system may be used to assist in diagnosing fuel system leaks rather than only relying on vacuum generated in the fuel system for leak testing. For example, by basing leak diagnostics on both pressure increases and vacuum increases in a fuel system, robustness and accuracy of leak diagnostics of a fuel system may be increased.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.